1. Field of the Invention
The present invention relates to a light guide and, more particularly, to a light guide for deflecting light rays from a light source to specific directions to control the light output angle.
2. Description of the Related Art
In recent years, small-size high-luminance power sources, such as light-emitting diodes (LEDs), have been widely used in various lighting devices. Although these lighting devices provide higher luminance, suitable light guides are still required to meet different light output patterns of various products by converting the light rays generated by the light sources into the desired light output patterns of the products. The light guides are used to deflect the light rays generated by the light sources to specific directions to thereby reduce the illuminating angle.
FIG. 1 shows a schematic view of a conventional light guide including a light-transmittable body 9. The body 9 includes a first end face 91, a second end face 92, a light emitting portion 93, a deflecting portion 94, and two lateral sides 95 and 96 connecting the light emitting portion 93 and the deflecting portion 94. The first end face 91 and the second end face 92 respectively form two ends of the body 9. The light emitting portion 93 is connected between the first and second end faces 91 and 92. The deflecting portion 94 is also connected between the first and second end faces 91 and 92. Preferably, the lighting emitting portion 93 and the deflecting portion 94 are opposite to each other.
In use of the conventional light guide, the first end portion 91 receives incident light rays from a light source 971 facing the first end face 91. The second end portion 92 receives light rays from another light source 972 facing the second end face 92. Alternatively, no light is incident to the second end face 92, and there is no need to provide the another light source 972. The light emitting portion 93 emits the light rays. The deflecting portion 94 includes a plurality of transversely extending inclined face structures 98. Each inclined face structure 98 includes a first deflecting face 981 and a second deflecting face 982. The first deflecting face 981 of each inclined face structure 98 faces the second deflecting face 982 of an adjacent inclined face structure 98, such that the first deflecting faces 981 and the second deflecting faces 982 are alternately disposed along the deflecting portion 94 to form a serrated structure. The deflecting portion 94 deflects the light rays to the light emitting portion 93, such that the light rays can be emitted via the light emitting portion 93. The two lateral sides 95 and 96 deflect the light rays back into an interior of the body 9, keeping the light rays inside the body 9 while moving forward until the light rays are emitted via the light emitting portion 93.
FIG. 2 shows the light path of the conventional light guide. A first reference light path L91 is a path of a light ray from the light source 971 that directly hits the first deflecting face 981a after transmitting the first end face 91, and after refection by the first deflecting face 981a, the light ray turns and emits via the light emitting portion 93. A second reference light path L92 is a path of a light ray from the light source 971 that transmits the first end face 91, that is deflected many times in the body 9, and that finally hits another first deflecting face 981z and is subsequently reflected by another first deflecting face 981z, turning the light ray to the light emitting portion 93 where the light ray is emitted. The light source 971 faces the first end face 91. Since the first deflecting face 981a providing reflection in the first reference light path L91 is located adjacent to the first end face 91, the occurrence probability of the first reference light path L91 is high, and the luminance is high. On the other hand, since another first deflecting face 981z in the second reference light path L92 is distant to the first end face 91 and, thus, has a low occurrence probability, the luminance is low. Thus, the luminance distribution of the whole light emitting portion 93 is not uniform. A portion of the light emitting portion 93 adjacent to the first end face 91 could be brighter, and another portion of the light emitting portion 93 distant to the first end face 91 could be darker. If another light source 972 is provided to generate a light ray incident to the second end face 92, the two end portions of the light emitting portion 93 could be brighter, and the central portion of the light emitting portion 93 distant to the first and second end faces 91 and 92 could be darker, also resulting in a non-uniform luminance distribution.
FIG. 3 shows another light path in a portion of the body 9 of the conventional light guide. After the light ray from the light source 971 has transmitted into the body 9 via the first end face 91, the light ray is deflected many times and moves towards the second end face 92 in irregular directions. A third reference light path L93 is a path of a light ray from the light source 971 that directly hits one of the first deflecting faces 981 adjacent to the central area, and after refection by the first deflecting face 981, the light ray turns to the light emitting portion 93 to successfully emit the light ray.
A fourth reference light path L94 is a path of a light ray that directly hits an area of the first deflecting face 981 away from the center, and after refection by the first deflecting face 981, the light ray turns and emits via the light emitting portion 93, resulting in a deviation of the angle while the light ray transmits the light emitting portion 93. Thus, a deviation angle A91 exists between the light emitting directions of the fourth reference light path L94 and the third reference light path L93. Namely, since both the third reference light path L93 and the fourth reference light path L94 exist in the body 9 and since a deviation angle A91 exists between the light emitting directions of the third and fourth reference light paths L93 and L94, the illuminating angle of the light emitting portion 93 is larger and, thus, could not meet the requirements of the light output patterns of specific products.
Furthermore, a fifth reference light path L95 is a path of a light ray that hits an area of the first deflecting face 981 adjacent to the lateral side 96, and after reflection by the first deflecting face 981, the light ray turns to the lateral side 96. When the angle between the light ray and the lateral side 96 is too large (approximating 90°), the light ray will directly transmit outside of the body 9 via the lateral side 96. Thus, light leakage occurs in the lateral sides 95 and 96 of the conventional light guide.
Furthermore, with reference to FIG. 4, a secondary reflection principle is used to improve the uniform luminance distribution of the light emitting portion 93. A sixth reference light path L96 is a path of a light ray transmitting the first end face 91, hitting and passing through the first deflecting face 981 of one of the inclined face structures 98, passing through the second deflecting face 982 of the inclined face structure 98 to the first deflecting face 981 of another inclined face structure 98, and reflected by the first deflecting face 981 of the another inclined face structure 98, turning the light ray to the light emitting portion 93 where the light ray is emitted. Namely, the light ray transmits the deflecting portion 94 via the first deflecting face 981 of the inclined face structure 98 and is subsequently incident into the interior of the body 9 via the second deflecting face 982 of the inclined face structure 98 to be incident to the first deflecting face 981 of another inclined face structure 98, forming a secondary reflection. However, although the secondary reflection can effectively reduce the non-uniform luminance distribution of the light emitting portion 93, the light ray might not be able to return to the interior of the body 9 after transmitting the deflecting portion 94, such that the light ray could directly be emitted to outside of the body 9, causing light leakage at the deflecting portion 94.
In view of the foregoing, since the existence of the first and second reference light paths L91 and L92 causes non-uniform luminance at the light emitting portion 93 that leads to inferior light emitting quality, since the existence of the third and fourth reference light paths L93 and L94 causes an enlarged illuminating angle of the light emitting portion 93 that leads to incapability of application on most lighting devices due to the large illuminating angle of the conventional light guide, and since the existence of the fifth and sixth reference light paths L95 and L96 causes light leakage at the lateral portion 96 or the deflecting portion 94 that leads to a reduction in the light guiding efficiency, improvement to the conventional light guide is necessary.